Panasonic is probably the best bang for the buck in plasma, but I prefer Samsung for picture quality -- admittedly, not by much, you probably can't go wrong with either choice.
Ditto Sony vs. Samsung vs. Sharp for LCD.
I mean, it's getting to the point where they all are really close.
And ditto on watching TV by day -- probably should go LCD or LED-backlit LCD.
And I, too, am waiting for certain improvements -- OLED and 3D, myself. I'm looking at just getting something 42"-46" 1080p 120Hz/240Hz/600Hz for the interim.
Your single best improvement will be to go 1080p from 720p, so make sure you get that, even if you don't increase size. I'd also try to get at least 120Hz. That's probably the single biggest step (from 60Hz to 120Hz) in the range (60-120, 120-240, 240-600).